DO CATHEDRAL GLASSES FLOW? Reportedly some stained glass windows from 12th century cathedrals are thicker at the bottom than at the top, suggesting that glass is a liquid which flows (albeit slowly) downward under the force of gravity. Surprisingly, the scientific literature on this point is scant, and Edgar Zanotto at the Federal University of Sao Carlos in Brazil (dedz@power.ufscar.br) investigated this issue by modeling several different kinds of glass. He determines that if glass flows it must do so on a time scale of billions of years and not mere centuries. Zanotto points out that glass vases several thousands of years old do not show the effect of any downward flow. He argues that some cathedral glasses might be larger at the bottom because of the old manufacturing process in which the glasses were blown into cylinders and then flattened manually. (American Journal of Physics, May 1998.)